In many conventional types of pumping systems used in a drilling apparatus, controlling and optimizing the performance of a sucker-rod pumping apparatus involves inherent difficulties. One factor which must be taken into account is the stretching of the rod string, which occurs during the upward portion of each pump stroke, and the corresponding contraction of the rod string which occurs during the downward portion of each pump stroke. The rod string, which may be 1000 feet or more long, acts much like an extension spring, which is stretched during the portion of the pump stroke in which the rod string is drawing the fluid upward within the well, and which then contracts back to an essentially un-stretched state as the rod string moves downward during a return portion of the pump stroke. As a result of the rod stretch, an above-ground upward stroke of 32 inches, for a well approximately 1300 feet deep, may only result in a down-hole stroke in the range of 24 to 26 inches, for example. The difference between the magnitude and direction of movement of the pump rod at the top of the well and the corresponding reaction of the rod string and down-hole stroke of the pump involves other complicating factors, including inherent damping within the rod string, fluid damping which occurs during the pump stroke and longitudinal vibrations and natural frequencies of the rod string.
The problems associated with effectively and efficiently operating a sucker-rod pump apparatus are addressed in significantly greater detail in a commonly assigned U.S. Pat. No. 7,168,924 B2, to Beck et al., titled “Rod Pump Control System Including Parameter Estimator”, the entire teachings and disclosure of which is incorporated herein by reference thereto. The Beck et al. patent also discloses a rod pump control system, which includes a parameter estimator that determines, from motor data, parameters relating to operation of the rod pump and/or generating a down-hole dynamometer card, without the need for external instrumentation such as down-hole sensors, rod load sensors, flow sensors, acoustic fluid level sensors, etc. In some embodiments disclosed by Beck et al., having a pumping apparatus driven by an electric motor, instantaneous current and voltage, together with pump parameters estimated through the use of a computer model of the sucker-rod pump, are used in determining rod position and load. The rod position and load are used to control the operation of the rod pump to optimize operation of the pump. Beck et al. also discloses a pump-stroke amplifier that is capable of increasing pump stroke without changing the overall pumping speed, or in the alternative, maintaining the well output with decreased overall pumping speed.
The inherent difficulties of operating a sucker-rod pump apparatus may also be compounded by the type of pumping apparatus, such as the typical walking-beam-type apparatus. The problems encountered when using these conventional pumping systems serve as ample evidence of the desirability of providing a new and improved pumping apparatus for use with a sucker-rod pump.
For example, conventional walking beam-type pumping mechanisms must typically be mounted on a heavy concrete foundation, which may be poured in place or pre-cast, located adjacent the well head. Construction of a walking beam pumping mechanism, together with its foundation, typically involves the efforts of several construction workers, over a period which may be a week or more, to prepare the site, lay the foundation, and allow time for the foundation to cure, in addition to the time required for assembling the various components of the walking beam mechanism onto the foundation and operatively connecting the mechanism to the pump rod.
Because of the costs of transporting the apparatus and the concrete or pre-cast foundation to what may be a remote site and the complexity of the site preparation and assembly process, walking beam-type pumping mechanisms are generally only utilized in long-term pumping installations. Further, the large size and massive weight of the walking beam pumping mechanism and its foundation may also problematic when the well is decommissioned. Economic and contractual obligations may require complete removal of the walking beam mechanism and its foundation.
Linear rod pumping systems have been developed to address a number of the above-described problems with conventional pumping systems. Linear rod pumping systems are disclosed in U.S. Pat. Nos. 8,152,492 and 8,641,390 both issued to Beck et al., and both titled “Linear Rod Pump Apparatus and Method”, the entire teachings and disclosures of which are incorporated herein by reference thereto.
Embodiments of the present invention represent an advancement over the state of the art in pumping systems. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.